
#1
Dec1510, 12:21 PM

P: 3

Not sure if the title does this question justice. My question how much energy in KWHs or a fraction thereof, could be saved in refrigerator operation if someone took a gallon of water, let it freeze solid outside during a 0F degree night, then placed it in their refrigerator until it thawed to around 35F… roughly the ambient temperature in the fridge.
Thanks! 



#2
Dec1510, 12:47 PM

P: 474

The energy needed to heat a material is Q = mcT
m is the mass, T is the temperature change and c is the specific heat capacity (in metric units water=4.2KJ/kg/deg C ice=2KJ/kg/deg C) Then the energy needed to melt the ice (and so the energy given out when ice melts) is called the latent heat of fusion ( 334 kJ/kg for ice>water) 



#3
Dec1510, 01:02 PM

P: 3





#4
Dec1510, 01:44 PM

P: 474

energy required to thaw one gallon of ice
Ok working in metric  cos I don't know the numbers for lbs/fahenheit etc
To heat 1 kg of ice from 18C (approx 0f) to 0C gives Q = 1Kg * 2KJ/kg/degC * 18degC = 36KJ To melt 1 kg of ice gives Q = 1Kg * 334 KJ/kg = 334KJ Then heating the water form 0C to 2C (ie 35F) gives Q = 1Kg * 4.2KJ/kg/degC * 2C = 8.4KJ So overall you get 36KJ + 334KJ + 8.4KJ = 378KJ 378/3600 = 0.1 KWh 



#5
Dec1510, 02:01 PM

P: 3





#6
Dec1510, 03:01 PM

P: 351

Anecdotally, my experience with coolers is that if you were to replace a gallon's worth of ice on a daily basis they should be able to keep cool indefinitely. While refrigerators are larger, it suggests to me that it could, at least, help. It would be rather easy to test with an experiment. Measure the refrigerator's energy consumption for a week, then add a gallon of ice every day for a week and measure it again. 



#7
Dec1510, 07:39 PM

Mentor
P: 22,001




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